See:
Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Black Rot
Cause Xanthomonas campestris pv. campestris is a bacterium that overwinters in plant refuse for up to 2 years and is carried internally and externally on seed. The bacterium infects other crucifer crops and weeds. It may be spread in the field by water (rain, irrigation), insects, equipment, and animals. Many outbreaks can be attributed to disease spread in the seedbed. When spread by water, bacteria enter water pores (hydathodes) at leaf margins or occasionally through insect or other mechanical injuries. From the leaf, the infection proceeds up and down the main stem and then becomes systemic. Disease development may stop in unfavorable weather only to resume when conditions are favorable. Optimum temperatures for development are 80°F to 86°F. Water in the form of dew, rain, or sprinkler irrigation is necessary for spread.
Symptoms Tissues at leaf margins become yellow; chlorosis progresses toward the leaf center, creating a V-shaped area with the base of the "V" at the leaf midrib. Veins in these areas become dark brown or black; when the leaf is held up to a strong light source, they show up as a black net. Vascular tissue of the main stem then becomes blackened. As the infection becomes systemic, symptoms (the same as those found from direct infection) may appear anywhere on the plant. Unilateral stunting of some leaves occurs. In infected seed, the first symptoms appear on cotyledons, which rapidly wilt and drop off; usually however, the infection has reached the stem and proceeds up.
Cultural control
- Use clean, pathogen-free seed. Seed from Western States generally is free from this disease.
- Use a 2-year rotation out of crucifers in production fields.
- Use a 3-year rotation in the transplant bed.
- Contaminated seed can be cleaned by hot water seed treatment of 122°F for 30 min.
- Control cruciferous weeds and insect pests.
- The cabbage varieties, Bobcat, Defender, and Guardian, are resistant.
- The following cabbage varieties have been rated for tolerance to black rot in a recent study at Cornell University.
- Low tolerance varieties: Bravo, Hinova, Little Rock, Renova, Stonar, Zerlina.
- Medium tolerance varieties: Atria, Bartolo, Green Winter, Krautking, Krautpacker, Lennox, Polinius, Protector, Rodolfo, Superelite.
- High tolerance varieties: King Cole, Roundup, Superdane, Superkraut, Titanic 90.
Chemical control
- Actigard at 0.5 to 1 oz/A every 7 days for up to four (4) applications per season can suppress the development of black rot by inducing host-resistance pathways. Do not apply within 7 days of harvest. 12-hr reentry.
- Badge SC (Group M1) at 0.5 to 1.8 pints/A on 7- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for green-house use; 48-hr reentry for all other applications.
- Champ WG (Group M1) at 1.06 lb/A on 7- to 10-day intervals. 48-hr reentry. O
- Cuprofix Ultra 40 Disperss (Group M1) at 0.75 to 1.25 lb/A on 7- to 10-day intervals. 48-hr reentry.
- Kocide 2000 (Group M1) at 0.75 to 1.5 lb/A or Kocide 3000 at 0.5 to 0.75 lb/A on 7- to 10-day intervals. 48-hr reentry. O
- Nu-Cop 50 DF (Group M1) at 1 lb/A on 7-day intervals for cabbage only. 48-hr reentry. O
- Previsto (Group M1) at 0.75 to 2 quarts/A on 7- to 10-day intervals. 48-hr reentry. O
- Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 5- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
Biological control Efficacy unknown in Oregon.
- Cease at 3 to 6 quarts in 100 gal water. For greenhouse plants only. Preharvest interval is 0 days. 4-hr reentry. O